Abstract

In the last decade there has been an increasing attention on the use of highly- and weakly- nonlinear solitary waves in engineering and physics, such as shock mitigation, acoustic imaging and nondestructive evaluation. These waves can form and travel in nonlinear systems such as one-dimensional chains of particles. One engineering application of solitary waves is the fabrication of acoustic lenses. In this dissertation, an acoustic lens based on the propagation of highly nonlinear solitary waves is proposed. The lens is part of a novel energy harvester able to focus mechanical vibrations into a single point where a piezoelectric element converts the mechanical energy into electricity.The first step of this research was to investigate numerically and experimentally a novel acoustic lens composed by one-dimensional chains of spherical particles arranged to form a circle array in contact with a linear medium. The second step of the research was to incorporate the acoustic lens into an energy harvesting that includes a wafer-type lead zirconate titanate (PZT) transducer and an object tapping the array. The PZT transducer located at the designed focal point converts the mechanical energy carried by the stress waves into electricity to power a load resistor.The performance of the designed harvester was compared to a conventional non-optimized cantilever beam, and the results showed that the power generated with the nonlinear lens has the same order of magnitude of the beam. Moreover, the performance of the proposed harvester was compared to a similar system where the chains of particles were replaced by solid rods. The results demonstrated that the granular system generates more electricity. Moreover, some parametric studies were conducted to improve the harvesting performance of the proposed system. The materials and the geometry of the harvester were considered to enhance the power output of the harvester. Numerical models were built to predict the power output from harvesters designed with different materials and geometries. The design that produces the highest power output was selected as the best design. The best design was tested experimentally to validate the enhancement in energy harvesting capability as predicted in the previous numerical model.